1. Technical Field of the Invention
The present invention relates to methods and apparatuses for processing PFC (perfluorocarbon) and compounds thereof (HFC) in which part of PFC is replaced with hydrogen, and more particularly to methods and apparatuses for processing PFC that are used in a manufacturing process for semiconductor devices and liquid crystal apparatuses.
2. Prior Art
Conventionally, a semiconductor device that uses, for example, metal plugs has a structure in which contact holes are formed in a dielectric film and wirings above and below thereof are connected to one another through the contact holes, such that electrical circuits provided on both sides of dielectric film are connected to one another.
The semiconductor device having the structure described above is manufactured in the following manner. Namely, a first wiring is formed over a surface of a semiconductor substrate, and then a dielectric film of silicon oxide (SiO2) is provided as an interlayer dielectric film. Contact holes are formed in the dielectric film.
Then, a second wiring layer is formed. In this instance, the first wiring layer and the second wiring layer are connected together through the contact holes. It is noted that the interlayer dielectric layer is normally formed by a chemical vapor deposition method (hereafter referred to as a “CVD” method).
In recent years, a plasma CVD method is often used. In the plasma CVD method, surplus products (deposits) are generated within the chamber in areas other than a wafer on which films are formed. The surplus products may possibly come off the chamber and fall onto the wafer, which may affect the yield in manufacturing ICs.
Accordingly, upon completion of each process, one method in which PFC is introduced into the vacuum chamber to thereby remove (clean) the remaining products is widely used.
FIG. 4 shows a structure of a conventional apparatus for manufacturing semiconductor devices. The manufacturing apparatus 1 that removes the remaining products has a vacuum chamber 2 and a piping 3 installed in a succeeding stage of the vacuum chamber 2, as shown in FIG. 4 (1). A blowout mouth 4 that enables spraying water (H2O), a plasma process section 5 and a vacuum pump 6 are connected to the piping 3 in a succeeding stage of the vacuum chamber 2, in order to prevent the PFC whose GWP (global warming power coefficient) is several thousands to several tens of thousand times greater than that of carbon dioxide from directly being discharged into the atmosphere.
In other words, after the cleaning, H2O is added to the PFC, and then a plasma process is conducted under a reduced pressure (in a vacuum), to generate carbon dioxide and hydrogen fluoride according to the following formula:CF4+2H2O→CO2+4HF
Then, the gas is returned through the vacuum pump 6 to the atmosphere.
It is noted that, since hydrogen fluoride has a strong acidity, it is sufficiently diluted by nitrogen gas or the like and then discharged into the atmosphere.
Referring to FIG. 4 (2), a vacuum pump 6 and an incineration chamber 7 are provided in a succeeding stage of the vacuum chamber 2 through a piping 3. The PFC, which is returned to the atmospheric pressure from the reduced pressure by the use of the vacuum pump 6, is introduced into the incineration chamber 7, and reacts with oxygen that is introduced simultaneously with the PFC in the incineration chamber 7 as follows:CF4+O2→CO2+2F2
By this reaction, the PFC that is used to clean the vacuum chamber 1 is processed, such that it is prevented from being directly discharged into the atmosphere.
However, the manufacturing apparatuses described above have the following problems. Namely, in the manufacturing apparatus shown in FIG. 4 (1), hydrogen fluoride is generated by the reaction between carbon tetrafluoride and water.
As described above, since hydrogen fluoride has a strong acidity, it is likely to oxidize structural parts (that are made of metal) of the vacuum pump 6 that is disposed in the succeeding stage of the plasma process section 5. Also, since the plasma process section 5 is placed under a reduced pressure (vacuum) similar to the vacuum chamber 2, it is difficult to perform maintenance and inspection works.
On the other hand, in the manufacturing apparatus shown in FIG. 4 (2), the PFC is thermodynamically stable and bonding among the molecules is strong. Therefore, the incineration temperature in the incineration chamber 7 is required to be over 1200 ° C. (more preferably, over 1400 ° C.). Furthermore, to securely accomplish the reaction between CF4 and O2, a long heating time is required. As a result, the structure of the incineration chamber 7 is complicated and a large amount of fuel is required.
Also, the incineration chamber 7 that satisfies the conditions described above (the heating temperatures and heating time) is generally large in size, and therefore, its processing capability is substantially large compared to the amount of the PFC that is used for the cleaning. Therefore, when the incineration chamber 7 is used for the reaction of the PFC, nitrogen gas is used to sufficiently dilute the PFC, and thereafter it is introduced into the incineration chamber 7. However, as the nitrogen gas is added to the PFC, it is likely that NOx may be generated during the incineration.
Furthermore, when the incineration temperature is low, the reaction intermediates may recombine to thereby re-create PFC, which would likely lower the decomposition efficiency.
In view of the problems of the conventional art described above, it is an object of the present invention to provide methods and apparatuses for processing PFC, which does not damage the vacuum pump or does not require an incineration process, and in which maintenance and inspection works are readily performed.